AT&T has decided to back the wildly popular mobile payments service known as Square. The second largest cellular company in the United States announced it plans to carry Square’s card readers in 1,000 of its retail stores. This is another huge partnership landed by the top mobile payment leader, who recently inked a deal with Starbucks. Square has its readers already in 20,000 outlets across the country.

You can find the mobile payments startup in your local Walgreens, Staples, FedEx Office, Apple, Wal-mart, Best Buy, RadioShack, and Target. The AT&T deal is just icing on the cake when it comes to dominance, as it should give the company more attention from consumers and merchants who are shopping for mobile devices.

In discussing the AT&T deal, Jeffrey Kolovson, head of Retail Distribution at Square said in a release:

“AT&T stores are a convenient retail destination for purchasing Square Card Readers, offering entrepreneurs the ability to purchase all of the devices they need to run their business in one place.” He continued saying “Square Card Reader makes it easier than ever for businesses to get started and grow using only their mobile device.”

The company is growing at a rapid pace, hitting an astonishing 2 million people and businesses accepting credit cards with the service (up from 1 million last year), and is processing $6 billion in payments volume per year. That growth can only accelerate thanks its recent $275/month flat fee plan for small businesses making up to $250,000 per year. As usual, Square readers sell for $9.99 in stores, but there’s a $10 credit that every buyer can redeem back to their bank account.